diff --git a/pymongo/ismaster.py b/pymongo/ismaster.py
index 25d239475..145bbd151 100644
--- a/pymongo/ismaster.py
+++ b/pymongo/ismaster.py
@@ -111,6 +111,10 @@ class IsMaster(object):
     def max_wire_version(self):
         return self._doc.get('maxWireVersion', common.MAX_WIRE_VERSION)
 
+    @property
+    def election_id(self):
+        return self._doc.get('electionId')
+
     @property
     def is_writable(self):
         return self._is_writable
diff --git a/pymongo/server_description.py b/pymongo/server_description.py
index 3c0307580..1763e2e53 100644
--- a/pymongo/server_description.py
+++ b/pymongo/server_description.py
@@ -32,7 +32,8 @@ class ServerDescription(object):
         '_address', '_server_type', '_all_hosts', '_tags', '_replica_set_name',
         '_primary', '_max_bson_size', '_max_message_size',
         '_max_write_batch_size', '_min_wire_version', '_max_wire_version',
-        '_round_trip_time', '_is_writable', '_is_readable', '_error')
+        '_round_trip_time', '_is_writable', '_is_readable', '_error',
+        '_election_id')
 
     def __init__(
             self,
@@ -54,6 +55,7 @@ class ServerDescription(object):
         self._max_write_batch_size = ismaster.max_write_batch_size
         self._min_wire_version = ismaster.min_wire_version
         self._max_wire_version = ismaster.max_wire_version
+        self._election_id = ismaster.election_id
         self._is_writable = ismaster.is_writable
         self._is_readable = ismaster.is_readable
         self._round_trip_time = round_trip_time
@@ -106,6 +108,10 @@ class ServerDescription(object):
     def max_wire_version(self):
         return self._max_wire_version
 
+    @property
+    def election_id(self):
+        return self._election_id
+
     @property
     def round_trip_time(self):
         """The current average latency or None."""
diff --git a/pymongo/topology.py b/pymongo/topology.py
index e410a09f3..de3b34782 100644
--- a/pymongo/topology.py
+++ b/pymongo/topology.py
@@ -40,7 +40,8 @@ class Topology(object):
         topology_description = TopologyDescription(
             topology_settings.get_topology_type(),
             topology_settings.get_server_descriptions(),
-            topology_settings.replica_set_name)
+            topology_settings.replica_set_name,
+            None)
 
         self._description = topology_description
         # Store the seed list to help diagnose errors in _error_message().
diff --git a/pymongo/topology_description.py b/pymongo/topology_description.py
index 4f274da33..3e0dd2c71 100644
--- a/pymongo/topology_description.py
+++ b/pymongo/topology_description.py
@@ -28,7 +28,12 @@ TOPOLOGY_TYPE = namedtuple('TopologyType', ['Single', 'ReplicaSetNoPrimary',
 
 
 class TopologyDescription(object):
-    def __init__(self, topology_type, server_descriptions, replica_set_name):
+    def __init__(
+            self,
+            topology_type,
+            server_descriptions,
+            replica_set_name,
+            max_election_id):
         """Represent a topology of servers.
 
         :Parameters:
@@ -36,10 +41,12 @@ class TopologyDescription(object):
           - `server_descriptions`: dict of (address, ServerDescription) for
             all seeds
           - `replica_set_name`: replica set name or None
+          - `max_election_id`: greatest electionId seen from a primary, or None
         """
         self._topology_type = topology_type
         self._replica_set_name = replica_set_name
         self._server_descriptions = server_descriptions
+        self._max_election_id = max_election_id
 
         # Is PyMongo compatible with all servers' wire protocols?
         self._incompatible_err = None
@@ -96,7 +103,11 @@ class TopologyDescription(object):
         sds = dict((address, ServerDescription(address))
                    for address in self._server_descriptions)
 
-        return TopologyDescription(topology_type, sds, self._replica_set_name)
+        return TopologyDescription(
+            topology_type,
+            sds,
+            self._replica_set_name,
+            self._max_election_id)
 
     def server_descriptions(self):
         """Dict of (address, ServerDescription)."""
@@ -111,6 +122,11 @@ class TopologyDescription(object):
         """The replica set name."""
         return self._replica_set_name
 
+    @property
+    def max_election_id(self):
+        """Greatest electionId seen from a primary, or None."""
+        return self._max_election_id
+
     @property
     def known_servers(self):
         """List of Servers of types besides Unknown."""
@@ -146,6 +162,7 @@ def updated_topology_description(topology_description, server_description):
     # TopologyDescription.
     topology_type = topology_description.topology_type
     set_name = topology_description.replica_set_name
+    max_election_id = topology_description.max_election_id
     server_type = server_description.server_type
 
     # Don't mutate the original dict of server descriptions; copy it.
@@ -156,7 +173,11 @@ def updated_topology_description(topology_description, server_description):
 
     if topology_type == TOPOLOGY_TYPE.Single:
         # Single type never changes.
-        return TopologyDescription(TOPOLOGY_TYPE.Single, sds, set_name)
+        return TopologyDescription(
+            TOPOLOGY_TYPE.Single,
+            sds,
+            set_name,
+            max_election_id)
 
     if topology_type == TOPOLOGY_TYPE.Unknown:
         if server_type == SERVER_TYPE.Standalone:
@@ -174,8 +195,8 @@ def updated_topology_description(topology_description, server_description):
             sds.pop(address)
 
         elif server_type == SERVER_TYPE.RSPrimary:
-            topology_type, set_name = _update_rs_from_primary(
-                sds, set_name, server_description)
+            topology_type, set_name, max_election_id = _update_rs_from_primary(
+                sds, set_name, server_description, max_election_id)
 
         elif server_type in (
                 SERVER_TYPE.RSSecondary,
@@ -190,8 +211,8 @@ def updated_topology_description(topology_description, server_description):
             topology_type = _check_has_primary(sds)
 
         elif server_type == SERVER_TYPE.RSPrimary:
-            topology_type, set_name = _update_rs_from_primary(
-                sds, set_name, server_description)
+            topology_type, set_name, max_election_id = _update_rs_from_primary(
+                sds, set_name, server_description, max_election_id)
 
         elif server_type in (
                 SERVER_TYPE.RSSecondary,
@@ -205,16 +226,21 @@ def updated_topology_description(topology_description, server_description):
             topology_type = _check_has_primary(sds)
 
     # Return updated copy.
-    return TopologyDescription(topology_type, sds, set_name)
+    return TopologyDescription(topology_type, sds, set_name, max_election_id)
 
 
-def _update_rs_from_primary(sds, replica_set_name, server_description):
+def _update_rs_from_primary(
+        sds,
+        replica_set_name,
+        server_description,
+        max_election_id):
     """Update topology description from a primary's ismaster response.
 
-    Pass in a dict of ServerDescriptions, current replica set name, and the
-    ServerDescription we are processing.
+    Pass in a dict of ServerDescriptions, current replica set name, the
+    ServerDescription we are processing, and the TopologyDescription's
+    max_election_id if any.
 
-    Returns (new topology type, new replica_set_name).
+    Returns (new topology type, new replica_set_name, new max_election_id).
     """
     if replica_set_name is None:
         replica_set_name = server_description.replica_set_name
@@ -223,7 +249,16 @@ def _update_rs_from_primary(sds, replica_set_name, server_description):
         # We found a primary but it doesn't have the replica_set_name
         # provided by the user.
         sds.pop(server_description.address)
-        return _check_has_primary(sds), replica_set_name
+        return _check_has_primary(sds), replica_set_name, max_election_id
+
+    if server_description.election_id is not None:
+        if max_election_id and max_election_id > server_description.election_id:
+            # Stale primary, set to type Unknown.
+            address = server_description.address
+            sds[address] = ServerDescription(address)
+            return _check_has_primary(sds), replica_set_name, max_election_id
+
+        max_election_id = server_description.election_id
 
     # We've heard from the primary. Is it the same primary as before?
     for server in sds.values():
@@ -247,7 +282,7 @@ def _update_rs_from_primary(sds, replica_set_name, server_description):
 
     # If the host list differs from the seed list, we may not have a primary
     # after all.
-    return _check_has_primary(sds), replica_set_name
+    return _check_has_primary(sds), replica_set_name, max_election_id
 
 
 def _update_rs_with_primary_from_member(
diff --git a/test/discovery_and_monitoring/rs/equal_electionids.json b/test/discovery_and_monitoring/rs/equal_electionids.json
new file mode 100644
index 000000000..3425668b4
--- /dev/null
+++ b/test/discovery_and_monitoring/rs/equal_electionids.json
@@ -0,0 +1,58 @@
+{
+    "description": "New primary with equal electionId", 
+    "phases": [
+        {
+            "outcome": {
+                "servers": {
+                    "a:27017": {
+                        "electionId": null, 
+                        "setName": null, 
+                        "type": "Unknown"
+                    }, 
+                    "b:27017": {
+                        "electionId": {
+                            "$oid": "000000000000000000000001"
+                        }, 
+                        "setName": "rs", 
+                        "type": "RSPrimary"
+                    }
+                }, 
+                "setName": "rs", 
+                "topologyType": "ReplicaSetWithPrimary"
+            }, 
+            "responses": [
+                [
+                    "a:27017", 
+                    {
+                        "electionId": {
+                            "$oid": "000000000000000000000001"
+                        }, 
+                        "hosts": [
+                            "a:27017", 
+                            "b:27017"
+                        ], 
+                        "ismaster": true, 
+                        "ok": 1, 
+                        "setName": "rs"
+                    }
+                ], 
+                [
+                    "b:27017", 
+                    {
+                        "electionId": {
+                            "$oid": "000000000000000000000001"
+                        }, 
+                        "hosts": [
+                            "a:27017", 
+                            "b:27017"
+                        ], 
+                        "ismaster": true, 
+                        "ok": 1, 
+                        "setName": "rs"
+                    }
+                ]
+            ]
+        }
+    ], 
+    "uri": "mongodb://a/?replicaSet=rs"
+}
diff --git a/test/discovery_and_monitoring/rs/new_primary_new_electionid.json b/test/discovery_and_monitoring/rs/new_primary_new_electionid.json
new file mode 100644
index 000000000..497f8f837
--- /dev/null
+++ b/test/discovery_and_monitoring/rs/new_primary_new_electionid.json
@@ -0,0 +1,117 @@
+{
+    "description": "New primary with greater electionId", 
+    "phases": [
+        {
+            "outcome": {
+                "servers": {
+                    "a:27017": {
+                        "electionId": {
+                            "$oid": "000000000000000000000001"
+                        }, 
+                        "setName": "rs", 
+                        "type": "RSPrimary"
+                    }, 
+                    "b:27017": {
+                        "electionId": null, 
+                        "setName": null, 
+                        "type": "Unknown"
+                    }
+                }, 
+                "setName": "rs", 
+                "topologyType": "ReplicaSetWithPrimary"
+            }, 
+            "responses": [
+                [
+                    "a:27017", 
+                    {
+                        "electionId": {
+                            "$oid": "000000000000000000000001"
+                        }, 
+                        "hosts": [
+                            "a:27017", 
+                            "b:27017"
+                        ], 
+                        "ismaster": true, 
+                        "ok": 1, 
+                        "setName": "rs"
+                    }
+                ]
+            ]
+        }, 
+        {
+            "outcome": {
+                "servers": {
+                    "a:27017": {
+                        "electionId": null, 
+                        "setName": null, 
+                        "type": "Unknown"
+                    }, 
+                    "b:27017": {
+                        "electionId": {
+                            "$oid": "000000000000000000000002"
+                        }, 
+                        "setName": "rs", 
+                        "type": "RSPrimary"
+                    }
+                }, 
+                "setName": "rs", 
+                "topologyType": "ReplicaSetWithPrimary"
+            }, 
+            "responses": [
+                [
+                    "b:27017", 
+                    {
+                        "electionId": {
+                            "$oid": "000000000000000000000002"
+                        }, 
+                        "hosts": [
+                            "a:27017", 
+                            "b:27017"
+                        ], 
+                        "ismaster": true, 
+                        "ok": 1, 
+                        "setName": "rs"
+                    }
+                ]
+            ]
+        }, 
+        {
+            "outcome": {
+                "servers": {
+                    "a:27017": {
+                        "electionId": null, 
+                        "setName": null, 
+                        "type": "Unknown"
+                    }, 
+                    "b:27017": {
+                        "electionId": {
+                            "$oid": "000000000000000000000002"
+                        }, 
+                        "setName": "rs", 
+                        "type": "RSPrimary"
+                    }
+                }, 
+                "setName": "rs", 
+                "topologyType": "ReplicaSetWithPrimary"
+            }, 
+            "responses": [
+                [
+                    "a:27017", 
+                    {
+                        "electionId": {
+                            "$oid": "000000000000000000000001"
+                        }, 
+                        "hosts": [
+                            "a:27017", 
+                            "b:27017"
+                        ], 
+                        "ismaster": true, 
+                        "ok": 1, 
+                        "setName": "rs"
+                    }
+                ]
+            ]
+        }
+    ], 
+    "uri": "mongodb://a/?replicaSet=rs"
+}
diff --git a/test/discovery_and_monitoring/rs/null_election_id.json b/test/discovery_and_monitoring/rs/null_election_id.json
new file mode 100644
index 000000000..90f66f6c9
--- /dev/null
+++ b/test/discovery_and_monitoring/rs/null_election_id.json
@@ -0,0 +1,107 @@
+{
+    "description": "Primary with no electionId, then a primary with electionId", 
+    "phases": [
+        {
+            "outcome": {
+                "servers": {
+                    "a:27017": {
+                        "electionId": null, 
+                        "setName": "rs", 
+                        "type": "RSPrimary"
+                    }, 
+                    "b:27017": {
+                        "electionId": null, 
+                        "setName": null, 
+                        "type": "Unknown"
+                    }
+                }, 
+                "setName": "rs", 
+                "topologyType": "ReplicaSetWithPrimary"
+            }, 
+            "responses": [
+                [
+                    "a:27017", 
+                    {
+                        "hosts": [
+                            "a:27017", 
+                            "b:27017"
+                        ], 
+                        "ismaster": true, 
+                        "ok": 1, 
+                        "setName": "rs"
+                    }
+                ]
+            ]
+        }, 
+        {
+            "outcome": {
+                "servers": {
+                    "a:27017": {
+                        "electionId": null, 
+                        "setName": null, 
+                        "type": "Unknown"
+                    }, 
+                    "b:27017": {
+                        "electionId": {
+                            "$oid": "000000000000000000000001"
+                        }, 
+                        "setName": "rs", 
+                        "type": "RSPrimary"
+                    }
+                }, 
+                "setName": "rs", 
+                "topologyType": "ReplicaSetWithPrimary"
+            }, 
+            "responses": [
+                [
+                    "b:27017", 
+                    {
+                        "electionId": {
+                            "$oid": "000000000000000000000001"
+                        }, 
+                        "hosts": [
+                            "a:27017", 
+                            "b:27017"
+                        ], 
+                        "ismaster": true, 
+                        "ok": 1, 
+                        "setName": "rs"
+                    }
+                ]
+            ]
+        }, 
+        {
+            "outcome": {
+                "servers": {
+                    "a:27017": {
+                        "electionId": null, 
+                        "setName": "rs", 
+                        "type": "RSPrimary"
+                    }, 
+                    "b:27017": {
+                        "electionId": null, 
+                        "setName": null, 
+                        "type": "Unknown"
+                    }
+                }, 
+                "setName": "rs", 
+                "topologyType": "ReplicaSetWithPrimary"
+            }, 
+            "responses": [
+                [
+                    "a:27017", 
+                    {
+                        "hosts": [
+                            "a:27017", 
+                            "b:27017"
+                        ], 
+                        "ismaster": true, 
+                        "ok": 1, 
+                        "setName": "rs"
+                    }
+                ]
+            ]
+        }
+    ], 
+    "uri": "mongodb://a/?replicaSet=rs"
+}
diff --git a/test/discovery_and_monitoring/rs/primary_disconnect_electionid.json b/test/discovery_and_monitoring/rs/primary_disconnect_electionid.json
new file mode 100644
index 000000000..8a4b42ced
--- /dev/null
+++ b/test/discovery_and_monitoring/rs/primary_disconnect_electionid.json
@@ -0,0 +1,154 @@
+{
+    "description": "Disconnected from primary, reject stale primary", 
+    "phases": [
+        {
+            "outcome": {
+                "servers": {
+                    "a:27017": {
+                        "electionId": null, 
+                        "setName": null, 
+                        "type": "Unknown"
+                    }, 
+                    "b:27017": {
+                        "electionId": {
+                            "$oid": "000000000000000000000002"
+                        }, 
+                        "setName": "rs", 
+                        "type": "RSPrimary"
+                    }
+                }, 
+                "setName": "rs", 
+                "topologyType": "ReplicaSetWithPrimary"
+            }, 
+            "responses": [
+                [
+                    "a:27017", 
+                    {
+                        "electionId": {
+                            "$oid": "000000000000000000000001"
+                        }, 
+                        "hosts": [
+                            "a:27017", 
+                            "b:27017"
+                        ], 
+                        "ismaster": true, 
+                        "ok": 1, 
+                        "setName": "rs"
+                    }
+                ], 
+                [
+                    "b:27017", 
+                    {
+                        "electionId": {
+                            "$oid": "000000000000000000000002"
+                        }, 
+                        "hosts": [
+                            "a:27017", 
+                            "b:27017"
+                        ], 
+                        "ismaster": true, 
+                        "ok": 1, 
+                        "setName": "rs"
+                    }
+                ]
+            ]
+        }, 
+        {
+            "outcome": {
+                "servers": {
+                    "a:27017": {
+                        "electionId": null, 
+                        "setName": null, 
+                        "type": "Unknown"
+                    }, 
+                    "b:27017": {
+                        "electionId": null, 
+                        "setName": null, 
+                        "type": "Unknown"
+                    }
+                }, 
+                "setName": "rs", 
+                "topologyType": "ReplicaSetNoPrimary"
+            }, 
+            "responses": [
+                [
+                    "b:27017", 
+                    {}
+                ]
+            ]
+        }, 
+        {
+            "outcome": {
+                "servers": {
+                    "a:27017": {
+                        "electionId": null, 
+                        "setName": null, 
+                        "type": "Unknown"
+                    }, 
+                    "b:27017": {
+                        "electionId": null, 
+                        "setName": null, 
+                        "type": "Unknown"
+                    }
+                }, 
+                "setName": "rs", 
+                "topologyType": "ReplicaSetNoPrimary"
+            }, 
+            "responses": [
+                [
+                    "a:27017", 
+                    {
+                        "electionId": {
+                            "$oid": "000000000000000000000001"
+                        }, 
+                        "hosts": [
+                            "a:27017", 
+                            "b:27017"
+                        ], 
+                        "ismaster": true, 
+                        "ok": 1, 
+                        "setName": "rs"
+                    }
+                ]
+            ]
+        }, 
+        {
+            "outcome": {
+                "servers": {
+                    "a:27017": {
+                        "electionId": {
+                            "$oid": "000000000000000000000003"
+                        }, 
+                        "setName": "rs", 
+                        "type": "RSPrimary"
+                    }, 
+                    "b:27017": {
+                        "electionId": null, 
+                        "setName": null, 
+                        "type": "Unknown"
+                    }
+                }, 
+                "setName": "rs", 
+                "topologyType": "ReplicaSetWithPrimary"
+            }, 
+            "responses": [
+                [
+                    "a:27017", 
+                    {
+                        "electionId": {
+                            "$oid": "000000000000000000000003"
+                        }, 
+                        "hosts": [
+                            "a:27017", 
+                            "b:27017"
+                        ], 
+                        "ismaster": true, 
+                        "ok": 1, 
+                        "setName": "rs"
+                    }
+                ]
+            ]
+        }
+    ], 
+    "uri": "mongodb://a/?replicaSet=rs"
+}
diff --git a/test/discovery_and_monitoring/single/direct_connection_external_ip.json b/test/discovery_and_monitoring/single/direct_connection_external_ip.json
index f0739c727..7ef5c6226 100644
--- a/test/discovery_and_monitoring/single/direct_connection_external_ip.json
+++ b/test/discovery_and_monitoring/single/direct_connection_external_ip.json
@@ -27,5 +27,5 @@
             ]
         }
     ], 
-    "uri": "mongodb://a/?connect=direct"
+    "uri": "mongodb://a"
 }
diff --git a/test/discovery_and_monitoring/single/direct_connection_mongos.json b/test/discovery_and_monitoring/single/direct_connection_mongos.json
index ef12c373f..51a396c0e 100644
--- a/test/discovery_and_monitoring/single/direct_connection_mongos.json
+++ b/test/discovery_and_monitoring/single/direct_connection_mongos.json
@@ -24,5 +24,5 @@
             ]
         }
     ], 
-    "uri": "mongodb://a/?connect=direct"
+    "uri": "mongodb://a"
 }
diff --git a/test/discovery_and_monitoring/single/direct_connection_rsarbiter.json b/test/discovery_and_monitoring/single/direct_connection_rsarbiter.json
index ec7458f28..3c3219b0b 100644
--- a/test/discovery_and_monitoring/single/direct_connection_rsarbiter.json
+++ b/test/discovery_and_monitoring/single/direct_connection_rsarbiter.json
@@ -28,5 +28,5 @@
             ]
         }
     ], 
-    "uri": "mongodb://a/?connect=direct"
+    "uri": "mongodb://a"
 }
diff --git a/test/discovery_and_monitoring/single/direct_connection_rsprimary.json b/test/discovery_and_monitoring/single/direct_connection_rsprimary.json
index e92d702fc..f864c0e04 100644
--- a/test/discovery_and_monitoring/single/direct_connection_rsprimary.json
+++ b/test/discovery_and_monitoring/single/direct_connection_rsprimary.json
@@ -27,5 +27,5 @@
             ]
         }
     ], 
-    "uri": "mongodb://a/?connect=direct"
+    "uri": "mongodb://a"
 }
diff --git a/test/discovery_and_monitoring/single/direct_connection_rssecondary.json b/test/discovery_and_monitoring/single/direct_connection_rssecondary.json
index 0dc2ecb64..d23833f1f 100644
--- a/test/discovery_and_monitoring/single/direct_connection_rssecondary.json
+++ b/test/discovery_and_monitoring/single/direct_connection_rssecondary.json
@@ -28,5 +28,5 @@
             ]
         }
     ], 
-    "uri": "mongodb://a/?connect=direct"
+    "uri": "mongodb://a"
 }
diff --git a/test/discovery_and_monitoring/single/direct_connection_slave.json b/test/discovery_and_monitoring/single/direct_connection_slave.json
index 1a38c5ca9..912e514a8 100644
--- a/test/discovery_and_monitoring/single/direct_connection_slave.json
+++ b/test/discovery_and_monitoring/single/direct_connection_slave.json
@@ -23,5 +23,5 @@
             ]
         }
     ], 
-    "uri": "mongodb://a/?connect=direct"
+    "uri": "mongodb://a"
 }
diff --git a/test/discovery_and_monitoring/single/direct_connection_standalone.json b/test/discovery_and_monitoring/single/direct_connection_standalone.json
index e066ce4f2..f4c40b13f 100644
--- a/test/discovery_and_monitoring/single/direct_connection_standalone.json
+++ b/test/discovery_and_monitoring/single/direct_connection_standalone.json
@@ -23,5 +23,5 @@
             ]
         }
     ], 
-    "uri": "mongodb://a/?connect=direct"
+    "uri": "mongodb://a"
 }
diff --git a/test/discovery_and_monitoring/single/unavailable_seed.json b/test/discovery_and_monitoring/single/unavailable_seed.json
index d5b31e1a1..09eb7fda1 100644
--- a/test/discovery_and_monitoring/single/unavailable_seed.json
+++ b/test/discovery_and_monitoring/single/unavailable_seed.json
@@ -20,5 +20,5 @@
             ]
         }
     ], 
-    "uri": "mongodb://a/?connect=direct"
+    "uri": "mongodb://a"
 }
diff --git a/test/test_discovery_and_monitoring.py b/test/test_discovery_and_monitoring.py
index 75b1a1667..c3900095f 100644
--- a/test/test_discovery_and_monitoring.py
+++ b/test/test_discovery_and_monitoring.py
@@ -14,13 +14,13 @@
 
 """Test the topology module."""
 
-import json
 import os
 import sys
 import threading
 
 sys.path[0:0] = [""]
 
+from bson import json_util
 from pymongo import common
 from pymongo.topology import Topology
 from pymongo.topology_description import TOPOLOGY_TYPE
@@ -175,7 +175,7 @@ def create_tests():
 
         for filename in filenames:
             with open(os.path.join(dirpath, filename)) as scenario_stream:
-                scenario_def = json.load(scenario_stream)
+                scenario_def = json_util.loads(scenario_stream.read())
 
             # Construct test from scenario.
             new_test = create_test(scenario_def)